1. Field of the Invention
The present invention relates to an intelligent machining system for machining a workpiece using a numerically controlled machine tool.
2. Description of the Prior Art
There has been a known automatic control system as shown in FIG. 16 for automatically determining machining conditions for a numerically controlled grinding machine, such as the rotating speed of a workpiece and the feed speed of the grinding wheel, on the basis of input conditions and fixed conditions to achieve desired machining results. For example, the rotating speed of the workpiece is determined automatically, as shown in FIG. 17, through the arithmetic processing of the input conditions by using theoretical formulas, empirical formulas and predetermined internal constants.
The input conditions, the fixed conditions and the machining conditions will inclusively be designated as static machining conditions.
The input conditions include the data of the workpiece including the materials, dimensions. allowances, surface roughness, dimensional accuracy and the like of the workpiece, and the data of the grinding wheel including the type and the like of the grinding wheel.
The fixed conditions are those relating to the numerically controlled grinding machine including the surface speed of the grinding wheel and the like.
The machining conditions include machining sequence, rotating speed of the workpiece, feed speed, machining allowances and dressing conditions.
The machining results include machining time, surface roughness, dimensional accuracy, roundness, burning, grinding crack, chatter and the like.
Variable conditions among the static machining conditions can be corrected after the automatic determination of the static machining conditions. The conditions thus corrected after automatic determination will be designated as corrected machining conditions. The static machining conditions and the corrected machining conditions will inclusively be designated as machining conditions.
Although many studies have been made to optimize machining conditions for grinding operation, machining conditions have not fully been elucidated.
Data provided by the automatic determination in the existing status of art is recognized merely as reference data, and the appropriate adjustment of the machining conditions for individual machining process requires the skill of the operator including intuition and experiences.
It is known empirically that the automatically determined machining conditions are not necessarily optimum conditions meeting the input conditions and fixed conditions. In practical machining operation, the automatically determined machining conditions are corrected on the basis of the empirical knowledge and intuition of the operator or the measurement of the workpiece machined according to the automatically determined machining conditions.
Since the correction of one of the machining conditions affects those of other machining conditions, the correction of the automatically determined machining conditions by the operator is considerably difficult.
Since the selection of machining conditions to be corrected and the determination of corrections for the machining conditions on the basis of machining errors determined by measuring the workpiece machined according to the predetermined machining conditions are dependent on the empirical skill and intuition of the operator, the correction made by the operator is not necessarily appropriate. Therefore, the machining of the workpiece according to corrected machining conditions, measurement of the workpiece and the recorrection of the corrected machining conditions must be repeated several times.
The current automatic machining condition determining method provides constant machining conditions in cases where provided that the input conditions and the fixed conditions are not changed; that is, the automatic machining condition determining method is of an open loop system which does not take the correction by the operator into consideration in the future automatic machining condition determination.
For example, even if the machining conditions are corrected properly by the operator, the rule for calculating the machining conditions is not changed for the future calculation of machining conditions. Accordingly, the operator is required to repeat the correcting operation for the determination of the same machining conditions.
The determination of the corrected machining conditions is not assisted by any numerical controller, but requires the technical skill of the operator including intuition and experiences.
During the grinding operation, machining circumstances including the abrasion of the grinding wheel, the thermal deformation of the parts of the grinding machine and the qualitative condition of the workpiece vary from time to time and affect the machining results significantly.
Accordingly, even if the static machining conditions or the corrected machining conditions are optimum machining conditions at the start of the machining operation, they are not necessarily optimum machining conditions throughout the machining operation because machining circumstances vary with time.